Although ranges may vary depending on the reference range a lab uses and the patient's age, normal levels of blood urea nitrogen are typically from 7 to 20 milligrams per deciliter of blood, according to Mayo Clinic. A high BUN level usually means the kidneys are not working properly.
Other causes of elevated BUN levels include urinary tract obstruction, gastrointestinal bleeding, dehydration or severe burns, states Mayo Clinic. BUN levels also may elevate in response to corticosteroids, certain antibiotics or a high protein diet. Patients who have had a recent heart attack or are experiencing congestive heart failure also exhibit higher BUN levels.